1. Field of the Invention
The invention relates to the field of lighter-than-air vehicles and, in particular, to cargo compartments for such vehicles.
2. Description of Related Art
Lighter-than-air vehicles have either non-rigid or rigid gasbags. There are three general types of non-rigid vehicles: those comprising a single gas filled bag; several gasbags joined together in series; and, of course, those having a multiple number gasbags within a non-rigid envelope. Rigid airships have an internal structure defining the shape of the vehicle containing a plurality of gasbags with an aerodynamic cover there over. One of the problems with both rigid and non-rigid lighter-than-air vehicles is their limited ability to station keep and/or maneuver when docking, especially if there are any significant cross-winds. This is primarily due to their large cross-sectional area, which causes the vehicle to "weather vane" and "wave" with the wind. They are particularly difficult to control if the wind is gusting or when there are significant up or down drafts. In fact, docking has proven to be the most difficult portion of a flight for a lighter-than-air-vehicle. Thus the most common docking procedure is moor the vehicle by its nose and let it weather vane.
In non-rigid designs the cargo flight station and cargo compartments are suspended from the bottom of the vehicle in what is most often referred to as a gondola. In rigid designs, it is also common practice to mount the flight station/passenger and cargo compartments under the gasbag. Unlike a conventional aircraft, the lift forces developed by the gasbag remains when docked. Thus as cargo is unloaded, the net lift force increases. In the past, this increase in net lift has been absorbed by docking restraints, for example mooring lines. If the cargo weight is very large, the force exerted on the mooring lines also becomes large and "station keeping" when docked becomes even more difficult. Therefore, unloading and reloading of cargo sometimes must wait until any winds have sufficiently died down or additional mooring lines must be used to "lock" the vehicle in one position. It is therefore obvious that it is always important to minimize the time spent in such operations.
Thus conventional loading of cargo containers and the like through doors located on the side of the vehicle is too slow and it would be difficult to simultaneously load and unload cargo in order to maintain the gross weight of the vehicle constant. Cargo aircraft, such as the C-5 military transport, have front and rear opening doors to the cargo compartment. However, moving the cargo simultaneously in the front and out the rear of a large lighter-than-air vehicle would still be a difficult and time consuming operation, especially if the cargo compartment is some 600 to 800 feet long. In addition, requiring an uninterrupted passageway over such a length would greatly complicate the design of the gondola. The use of individual cargo compartments located along either side of the vehicle can reduce the cargo loading and unloading time, but does not address the need to maintain a constant payload weight on the vehicle. In U.S. Pat. No. 5,143,323, "Airship Handling System" by F. Husain, et al. a vehicle is disclosed having a cargo/passenger module that is secured in a recess in the gondola. However, properly securing such a module to the gondola is believed to complicate the design of the gondola. In addition, the cargo module would have to be flight certified increasing its cost. In fact, no prior art cargo compartment design has addressed the need to maintain a constant payload weight during loading and unloading of cargo and/or to provide a cargo loading system that minimizes the docking time for unloading and loading cargo.
Therefore, it is a primary object of the invention to provide a cargo compartment for a lighter-than-air vehicle that allows a constant neutral buoyancy to be maintained on the vehicle during loading and unloading thereof.
It is another primary object of the invention to provide a cargo compartment for a lighter-than-air vehicle that provides for simultaneous loading and unloading of cargo while maintaining a constant neutral buoyancy on the vehicle.
It is a further object of the invention to provide a cargo compartment for a lighter-than-air vehicle wherein the cargo can be loaded and unloaded using individual cargo containers.